Updated splitAtLineCol to use Maybe

Author: gusosim

src/Data/Rope.hs

@@ -123,18 +123,20 @@ splitAtPositionR8 (Rope8.Position initPL initPC) rope = do
     x : _ -> x
     [] -> (mempty, rope) -- should be unreachable, as one of the tried positions should split the string neatly
 
--- TODO: return a maybe
-splitAtLineCol :: LineCol -> Rope -> (Rope, Rope)
-splitAtLineCol (LineCol (Pos line) (Pos col)) (Rope rope) = (Rope before, Rope after)
+splitAtLineCol :: LineCol -> Rope -> Maybe (Rope, Rope)
+splitAtLineCol lineCol r
+  | isValidLineColEnd r lineCol = Just (Rope before, Rope after)
+  | otherwise = Nothing
  where
+  (LineCol (Pos line) (Pos col)) = lineCol
   (before, after) =
     splitAtPositionR8
       ( Rope8.Position
           { posLine = (fromIntegral line)
           , posColumn = (fromIntegral col)
           }
       )
-      rope
+      r.rope
 
 indexRange :: Rope -> Range -> Maybe Rope
 indexRange (Rope r) (Range (Pos start) (Pos end))

test/Data/RopeSpec.hs

@@ -24,36 +24,28 @@ spec = do
   describe "line col split at" do
     let check name t lineCol (before, after) = it name do
           let r = Rope.fromText t
-          let (before', after') = Rope.splitAtLineCol lineCol r
-          before' `shouldBe` before
-          after' `shouldBe` after
+          Rope.splitAtLineCol lineCol r `shouldBe` Just (before, after)
           pure @IO ()
 
     check "index past the line" "abcd\n1234" (LineCol (Pos 0) (Pos 4)) ("abcd", "\n1234")
 
     it "index on newline" do
       let t = "abcd\n1234"
       let r = Rope.fromText t
-      let (before, after) = Rope.splitAtLineCol (LineCol (Pos 0) (Pos 5)) r
-      before `shouldBe` "abcd\n"
-      after `shouldBe` "1234"
+      Rope.splitAtLineCol (LineCol (Pos 0) (Pos 5)) r `shouldBe` Just ("abcd\n", "1234")
       pure @IO ()
 
     -- TODO: prevent the rope from doing this
     it "index past newline" do
       let t = "abcd\n1234"
       let r = Rope.fromText t
-      let (before, after) = Rope.splitAtLineCol (LineCol (Pos 0) (Pos 6)) r
-      before `shouldBe` "abcd\n1"
-      after `shouldBe` "234"
+      Rope.splitAtLineCol (LineCol (Pos 0) (Pos 6)) r `shouldBe` Nothing 
       pure @IO ()
 
     it "index past newline" do
       let t = "abcd\n1234\n"
       let r = Rope.fromText t
-      let (before, after) = Rope.splitAtLineCol (LineCol (Pos 2) (Pos 0)) r
-      before `shouldBe` "abcd\n1234\n"
-      after `shouldBe` ""
+      Rope.splitAtLineCol (LineCol (Pos 2) (Pos 0)) r `shouldBe` Just ("abcd\n1234\n", "")
       pure @IO ()
 
     it "convert line col at the end" do